Are you going to attempt elite status? If so, your only chance is to go Delta. Unfortunately northwest does not give elite qualifying miles to China Airlines flights.

Also, consider what fare bucket you are in as Northwest doesn't give full redeemable miles for many fares.

http://www.nwa.com/worldperks/earn/a...shtml#chinaair

Earning Banked Miles
100% of actual miles flown (500-mile minimum): F, A, J, C, D, Y, B, M, T
80% of actual miles flown (500-mile minimum): K, Q
60% of actual miles flown (500-mile minimum): H, N
Miles not earned in the following classes: L, X, G, V, W, Z, E, U, R, I, O, S

China Airlines flights do not count towards Elite qualification.